Alpha stabilized black titanium alloys

ABSTRACT

A titanium alloy having a Ti—Zr—X—Y formulation, wherein the X component is a Group V or Group VI metal and the Y component is an alpha stabilizer selected from aluminum, tin, silicon, oxygen, carbon, and nitrogen, where the titanium alloy is capable of being blackened in an air, oxygen, or oxygen containing environment. The alloy may have a yield strength of at least 100 ksi. The Y component may be oxygen above 1300 ppm. The Zr content may be greater than 22 weight percent. The alloy may have a lightness index of 46 or less on the CIELAB scale.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims benefit of U.S. Provisional PatentApplication Ser. No. 62/463,752 filed Feb. 27, 2017, the disclosure ofwhich is hereby incorporated by reference herein

BACKGROUND OF THE INVENTION

The term “black titanium” is used to describe titanium-based alloyscontaining enough zirconium to form a black oxide layer when the alloyis heated in environments containing air, oxygen, or nitrogen. Thisoxide layer can increase the wear resistance or the aesthetic appeal ofthe titanium surface, and articles formed through these processes havefound wide commercial acceptance due in part to the aesthetic appeal ofthe black or blue/black appearance of the oxide layer. Further, theoxide layer can improve the coefficient of friction and other propertiesof the titanium alloy surface.

BRIEF SUMMARY OF THE INVENTION

Although well received, it would be beneficial to create a material withimproved characteristics.

In accordance with an embodiment of the invention, there is provided atitanium alloy comprising a Ti—Zr—X—Y formulation, wherein X is a GroupV or Group VI metal and Y is an alpha stabilizer selected from aluminum,tin, silicon, oxygen, carbon, and nitrogen; and, wherein said titaniumalloy is capable of being blackened in an air, oxygen, or oxygencontaining environment.

In accordance with an embodiment of the invention, there is provided atitanium alloy comprising a Ti—Zr—X—Y formulation, wherein X is a GroupV or Group VI metal and Y is an alpha stabilizer selected from aluminum,tin, silicon, oxygen, carbon, and nitrogen; and, wherein said titaniumalloy is capable of being blackened in an air, oxygen, or oxygencontaining environment; where the alloy has a yield strength of at least100 ksi.

In accordance with an embodiment of the invention, there is provided atitanium alloy comprising a Ti—Zr—X—Y formulation, wherein X is a GroupV or Group VI metal and Y is an alpha stabilizer selected from aluminum,tin, silicon, oxygen, carbon, and nitrogen; and, wherein said titaniumalloy is capable of being blackened in an air, oxygen, or oxygencontaining environment; where Y may be oxygen and an oxygen level of thealloy may be above 1300 ppm.

In accordance with an embodiment of the invention, there is provided atitanium alloy comprising a Ti—Zr—X—Y formulation, wherein X is a GroupV or Group VI metal and Y is an alpha stabilizer selected from aluminum,tin, silicon, oxygen, carbon, and nitrogen; and, wherein said titaniumalloy is capable of being blackened in an air, oxygen, or oxygencontaining environment; where the Zr content may be greater than 22weight percent.

In accordance with an embodiment of the invention, there is provided atitanium alloy comprising a Ti—Zr—X—Y formulation, wherein X is a GroupV or Group VI metal and Y is an alpha stabilizer selected from aluminum,tin, silicon, oxygen, carbon, and nitrogen; and, wherein said titaniumalloy is capable of being blackened in an air, oxygen, or oxygencontaining environment; where the Zr content may be greater than 25weight percent.

In accordance with an embodiment of the invention, there is provided atitanium alloy comprising a Ti—Zr—X—Y formulation, wherein X is a GroupV or Group VI metal and Y is an alpha stabilizer selected from aluminum,tin, silicon, oxygen, carbon, and nitrogen; and, wherein said titaniumalloy is capable of being blackened in an air, oxygen, or oxygencontaining environment; where a Zr content is between 20 and 35 weightpercent, the alloy further comprising aluminum.

In accordance with an embodiment of the invention, there is provided atitanium alloy comprising a Ti—Zr—X—Y formulation, wherein X is a GroupV or Group VI metal and Y is an alpha stabilizer selected from aluminum,tin, silicon, oxygen, carbon, and nitrogen; and, wherein said titaniumalloy is capable of being blackened in an air, oxygen, or oxygencontaining environment; where the titanium alloy has a lightness indexof 42 or less on the CIELAB scale.

In accordance with an embodiment of the invention, there is provided atitanium alloy comprising a Ti—Zr—X—Y formulation, wherein X is a GroupV or Group VI metal and Y is an alpha stabilizer selected from aluminum,tin, silicon, oxygen, carbon, and nitrogen; and, wherein said titaniumalloy is capable of being blackened in an air, oxygen, or oxygencontaining environment; where the titanium alloy has a lightness indexof 46 or less on the CIELAB scale.

In accordance with an embodiment of the invention, there is provided atitanium alloy comprising a Ti—Zr—X—Y formulation, wherein X is a GroupV or Group VI metal and Y is an alpha stabilizer selected from aluminum,tin, silicon, oxygen, carbon, and nitrogen; and, wherein said titaniumalloy is capable of being blackened in an air, oxygen, or oxygencontaining environment; where an aluminum equivalent of the alloy isless than approximately 10.

In accordance with an embodiment of the invention, there is provided atitanium alloy comprising a Ti—Zr—X—Y formulation, wherein X is a GroupV or Group VI metal and Y is an alpha stabilizer selected from aluminum,tin, silicon, oxygen, carbon, and nitrogen; and, wherein said titaniumalloy is capable of being blackened in an air, oxygen, or oxygencontaining environment; where a transus temperature of the alloy exceeds610° C.

In accordance with an embodiment of the invention, there is provided atitanium alloy comprising a Ti—Zr—X—Y formulation, wherein X is a GroupV or Group VI metal and Y is an alpha stabilizer selected from aluminum,tin, silicon, oxygen, carbon, and nitrogen; and, wherein said titaniumalloy is capable of being blackened in an air, oxygen, or oxygencontaining environment; where Y is oxygen and an oxygen level of thetitanium is between 1300 ppm and 4000 ppm.

In accordance with an embodiment of the invention, there is provided atitanium alloy comprising a Ti—Zr—X—Y formulation, wherein X is a GroupV or Group VI metal and Y is an alpha stabilizer selected from aluminum,tin, silicon, oxygen, carbon, and nitrogen; and, wherein said titaniumalloy is capable of being blackened in an air, oxygen, or oxygencontaining environment; where an oxygen level of the titanium is between1500 ppm and 3000 ppm.

In accordance with an embodiment of the invention, there is provided atitanium alloy comprising a Ti—Zr—X—Y formulation, wherein X is a GroupV or Group VI metal and Y is an alpha stabilizer selected from aluminum,tin, silicon, oxygen, carbon, and nitrogen; and, wherein said titaniumalloy is capable of being blackened in an air, oxygen, or oxygencontaining environment; where the alloy is 22 to 35 wt % Zr, 0 to 10 wt% Nb, 0 to 10 wt % Mo, 0 to 6 wt % Cr, 0 to 6wt % V, 0 to 5% wt % Al, 0to 6% Sn, 0.13 to 0.40 wt % O, with the balance titanium.

In accordance with an embodiment of the invention, there is provided atitanium alloy comprising a Ti—Zr—X—Y formulation, wherein X is a GroupV or Group VI metal and Y is an alpha stabilizer selected from aluminum,tin, silicon, oxygen, carbon, and nitrogen; and, wherein said titaniumalloy is capable of being blackened in an air, oxygen, or oxygencontaining environment; where the alloy is one ofTi-30Zr-2Mo-1.5Sn-0.18O, 30Zr-2Mo-1.5Sn-0.26O, Ti-30Zr-4Mo-1.5Sn-0.18O,30Zr-4Mo-1.5Sn-0.26O, Ti-35Zr-10Nb-0.24O, Ti-35Zr-10Nb-1Al-0.15O,Ti-35Zr-10Nb-2.5Al-0.23O, Ti-30Zr-10Nb-0.2O, Ti-30Zr-10Nb-2Al-0.21O,Ti-30Zr-10Nb-1Al-0.3O, Ti-30Zr-10Nb-0.5Al-0.22O,Ti-30Zr-10Nb-1.5Sn-0.20O, Ti-30Zr-10Nb-3Sn-0.28O,Ti-30Zr-10Nb-6Sn-0.20O, Ti-30Zr-3Cr-1.5Sn-0.25O, andTi-30Zr-6V-1.5Sn-0.25O.

In accordance with an embodiment of the invention, there is provided atitanium alloy comprising a Ti—Zr—X—Y formulation where the alloy iscapable of being blackened in an air, oxygen, or oxygen containingenvironment to a lightness value of 48 or lower on the CIELAB colorspace; wherein, Y is an alpha stabilizer selected from aluminum, tin,silicon, oxygen, carbon, and nitrogen; and wherein, X is a betastabilizer selected from niobium, chromium, molybdenum, and vanadium.

In accordance with an embodiment of the invention, there is provided atitanium alloy comprising a Ti—Zr—X—Y formulation where the alloy iscapable of being blackened in an air, oxygen, or oxygen containingenvironment to a lightness value of 48 or lower on the CIELAB colorspace; wherein, Y is an alpha stabilizer selected from aluminum, tin,silicon, oxygen, carbon, and nitrogen; and wherein, X is a betastabilizer selected from niobium, chromium, molybdenum, and vanadium;wherein when X is niobium, said alloy has a transus temperature ofapproximately 640° C. or greater; and when X is chromium, molybdenum, orvanadium, said alloy has a transus temperature of approximately 610° C.or greater.

In accordance with an embodiment of the invention, there is provided atitanium alloy comprising a Ti—Zr—X—Y formulation, wherein X is a GroupV or Group VI metal and Y is an alpha stabilizer selected from aluminum,tin, silicon, oxygen, carbon, and nitrogen; and, wherein said titaniumalloy is capable of being blackened in an air, oxygen, or oxygencontaining environment. In such an embodiment, the following featuresmay be included in all possible combinations: the alloy may have a yieldstrength of at least 100 ksi; Y may be oxygen and an oxygen level of thealloy may be above 1300 ppm; the Zr content may be greater than 22weight percent or 25 weight percent; the alloy may have a lightnessindex of 42 or less on the CIELAB scale or 46 or less on the CIELABscale; and/or the aluminum equivalent may be less than approximately 10;the transus temperature may exceed 610° C.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with features, objects, and advantages thereof, will be orbecome apparent to one with skill in the art upon reference to thefollowing detailed description when read with the accompanying drawings.It is intended that any additional organizations, methods of operation,features, objects or advantages ascertained by one skilled in the art beincluded within this description, be within the scope of the presentinvention, and be protected by the accompanying claims.

With respect to the drawings, FIG. 1 depicts a table providingspecifications for a specific titanium alloy described in theSpecification;

FIG. 2 depicts a graph showing the effects of zirconium content onlightness in a particular context described in the Specification;

FIG. 3 depicts a graph showing the blackening response of an aluminumstabilized material described in the Specification;

FIG. 4 depicts a table of mechanical performances for materialsdescribed in the Specification;

FIG. 5 depicts a table of mechanical performances for materialsdescribed in the Specification;

FIG. 6 depicts a graph showing the effect of different passivatingelements on a material described in the Specification; and,

FIG. 7 shows a table providing transus temperatures for certainmaterials described in the Specification.

DETAILED DESCRIPTION

In the following are described the preferred embodiments of the ALPHASTABILIZED BLACK TITANIUM ALLOYS in accordance with the presentinvention. In describing the embodiments illustrated in the drawings,specific terminology will be used for the sake of clarity. However, theinvention is not intended to be limited to the specific terms soselected, and it is to be understood that each specific term includesall technical equivalents that operate in a similar manner to accomplisha similar purpose. Where like elements have been depicted in multipleembodiments, identical reference numerals have been used in the multipleembodiments for ease of understanding.

Throughout this disclosure it is to be understood that the term“articles of manufacture” is to be construed broadly and is inclusive ofall manufactured articles which have conventionally been, or could be,formed from titanium using known techniques or techniques to bedeveloped. Such articles may be considered articles of ornamentation orcomponents therefor, such as fashion accessories, jewelry, eye glasses,watches, etc. Such articles may also be consumer products or componentstherefor, including wearable technology, phone components, firearms,etc. The articles may also be general mechanical components of anymanufactured device used as a consumer product, industrial components,or the like. They may also include medical applications such asimplantable devices or surgical instruments.

As discussed earlier, “black titanium” typically describestitanium-based alloys containing enough zirconium to form a black oxidelayer when the alloy is heated in environments containing air, oxygen,or nitrogen. Conventionally, such alloys contain titanium (“Ti”),zirconium (“Zr”), and a third alloying element (“X”) that serves topassivate the rapid oxidation of the surface allowing a controlledoxidation to take place. This is often referred to as a Ti—Zr—X formula.

It is to be understood that the term passivate means to cause the metalto be less prone to rapid oxidation by altering the surface or coatingthe surface with a thin inert layer.

The proposed mechanism fox passivation is the transport of oxygen intothe bulk of the Ti—Zr matrix through the third alloying elementconcentrated at the grain boundaries. Conventional wisdom proposed thatelements having high oxidizing agent transport properties should besuitable for the third alloying element.

Alloys of this nature have also been used to achieve materials with alower modulus. Indeed, titanium-based materials with a modulus close tobone are desirable for implanted prosthetic joints to reduce “stressshielding” caused by mis-matched modulus,

Articles of manufacture, including implant applications, utilize theTi—Zr—X formula for alloy composition. For general articles ofmanufacture, the X component acts as a passivator and in the implantapplication the X acts as a beta stabilizer and potentially apassivator, and if chosen correctly contributes to a lower modulus.

All of these alloys are classified as beta alloys. Beta alloys have alower beta transus than pure titanium, and typically need to be heattreated to develop optimal strength. This is a drawback because heattreatment adds expense and an opportunity for distortion of parts,adding further expense if additional machining or forming is required.

While titanium alloys have many desirable characteristics such asbiocompatibility, high strength-to-weight ratio, and corrosionresistance, they also have poor wear resistance when compared toconventional materials. A black oxide surface can greatly improve thewear resistance of titanium material and overcome this limitation.

Because of its desirable characteristics titanium has found wideacceptance in critical use markets such as medical, aerospace, anddefense. In these markets its lack of wear resistance has been overcomeby incorporating other materials on areas that need better wearperformance. Its adoption by consumer markets has been limited not onlyby the design burden of working around poor wear performance but alsoits high cost and difficulty in machining.

This invention overcomes these challenges by using improved blacktitanium alloys that enhance resultant mechanical properties, are moresuitable for processing via powder metallurgy methods than conventionalblack titanium materials, and which respond more favorably to theblackening process and other thermal treatments such as hydrogenchemical treatment. The ability to process high performance titaniumalloys via powder metallurgy can lower the manufacturing cost and thusincrease adoption by more price sensitive markets such as wearables,consumer electronics, sporting goods or eyewear.

Recent advances in titanium powder metallurgy have made the robustprocessing of complex high performance parts a reality. High performancetitanium powder metallurgy techniques rely on developing a process thatallows microstructural control and creates a final density that iseffectively completely dense. The best route for achieving a combinationof refined microstructure and high density is to sinter the article toclosed porosity and then densify the article completely via a hotisostatic pressing (“HIP,” “HIPing,” or “HIPed”) operation. Not allapplications require a HIPing step, but high-performance titanium alloysfor demanding applications are almost always preferred to be completelydense. When a titanium alloy is less than completely dense, it canbehave in a more brittle fashion and may also have much lower fatigueperformance.

The alloys described are readily fabricated via powder metallurgy usingany of the conventional forming techniques such as compaction, injectionmolding, extrusion or three-dimensional printing. Pre-alloy, masteralloy, or blended elemental powder routes are all suitable raw materialapproaches for these alloys. After forming the powder into the desiredshape, the article is sintered in an inert or vacuum atmosphere. Aftersintering the article may be hot isostatically pressed if higher densityis desired.

In the conventional black alloy having a Ti—Zr—X structure, X istypically chosen from a Group V or Group VI metal such, as vanadium,niobium, tantalum, chromium, molybdenum or tungsten. Typically, 5 atomicpercentage or more of a passivating element is added. All of thesematerials are strong beta phase stabilizers and because of this, all ofthe conventional black titanium alloys are classified as metastable betaalloys.

By also manipulating the black titanium alloy to stabilize and increasethe alpha phase, the mechanical properties of the as-sintered or HIPedproduct can be greatly improved by both an increased presence ofstrengthened alpha phase and strengthened beta phase in the finalproduct. Further, by stabilizing and increasing the alpha phase thetransus temperature is elevated. The elevated transus temperature canaid in thermo-chemical heat treatments as well as protect the alloy fromdegradation of mechanical properties due to thermal blackening cycles.In the black titanium system, the alpha phase is stabilized by addingoxygen, tin, aluminum, or other alpha stabilizers.

There are many considerations to the level of alpha stabilizer orpassivator used in an improved black titanium alloy composition. Inaddition to stabilizing the alpha phase via oxygen, tin, or aluminumadditions, it may be desirable to adjust the zirconium content slightlyto maintain the same color or blackening performance as well as allowingfor adjustments to the amounts of other alpha stabilizers to optimizestrength, wear, and cosmetic properties. With respect to zirconium,while it is an important consideration in determining the aluminumequivalent, it depresses the transus and from this perspective isconsidered a beta stabilizer. It is considered in the aluminumequivalent calculation because it concentrates the aluminum in theremaining titanium matrix. Aluminum, tin, oxygen, carbon, and nitrogenhave an alpha stabilizing role and their effectiveness relative toaluminum is described in the aluminum equivalency equation:

Aluminum equivalent, wt %=Al+⅓Sn+⅙Zr+10(O+C+2N)

It is generally accepted that care should be taken not to exceed analuminum equivalent approximately equal to 10. At high aluminumequivalent levels, detrimental precipitates, typically Ti₃X can form.Because of this there are limits to how much aluminum or other alphastabilizers may be effectively added. If it is desired to stabilize morealpha phase it may be necessary to lower the zirconium content to enablea rise in the alpha stabilizer content.

Many conventional black titanium articles are fabricated fromcommercially available Ti-35Zr-10Nb alloy. This alloy is marketed asTiadyne™ 3510 by Alleghany Technologies, Inc. of Pittsburgh, Pa. It isthe only commercial titanium alloy designed for blackening known to theinventors at this time. The specification for this alloy shown in thetable of FIG. 1.

Ti-35Zr-10Nb is a beta alloy. This is reflected in its low transustemperature of 635° C. Conventionally formed Ti-35Zr-10Nb alloy has ayield strength of 65 ksi when quenched from the beta annealed state.Working or heat treatment can be used to increase the yield strength tobetween 140-150 ksi. However, upon subjecting the material to a typicalblackening treatment of heating in air to 550° C. for two hours, theyield strengths are degraded to 120 ksi or lower. While the oxygen inthe specification could technically be considered an alpha stabilizer,the upper limit of 1300 ppm prevents it from substantially increasingthe strength of the material.

Powder forming routes for this alloy do not yield good results. Materialsubjected to a conventional HIP cycle exhibits a yield strength of 98ksi, a very low value for titanium alloys. Commercially, titanium alloysusually have a yield strength of over 100 ksi to find practicalapplication.

This invention improves the properties of black titanium alloys to notonly exceed the performance of the known alloys formed by powder methodsbut to provide better performance than the known alloys when processedin their optimal methods such as heat treating or working. This can beachieved by many different changes to the alloy chemistry.

Improved alloys will may have an increased transus temperature. Theelevated transus is indicative of greater amount of alpha in both theas-sintered product and the densified product. This increased alphacontent provides for better mechanical properties without the need formechanical working or further heat treatment. Additionally, the alloy'sperformance is not substantially degraded by the blackening process, andin some cases may be improved.

Because most alpha stabilizers will increase the transus temperaturewhen added to the typical Ti—Zr—X formulation, there are manypermutations of this improvement with respect to the actual formulationused. As a general rule, combinations of aluminum, tin, oxygen, carbon,or nitrogen as alpha stabilizers can be used to increase the transus,while reductions in beta stabilizing amounts or potency will also resultin an increase in the beta transus.

The Ti-35Zr-10Nb alloy has an oxygen limit of 1300 ppm. While thisallows for robust processing of the material by conventional methods,increasing the oxygen content in excess of this limit vastly improvesthe performance high zirconium alloys when processed using powdermetallurgy routes.

Oxygen is known to have an embrittling effect on titanium alloys andthis holds true for alloys of the Ti—Zr—X structure as well. However, abroad window exists for improving the powder metallurgy processabilityof these alloys that is above the current accepted oxygen limit andbelow the level that would impact functionality of the material. It hasbeen discovered that the limit could be increased by two to four-fold,depending on the level of other alpha stabilizers and the zirconiumlevel. Indeed, oxygen content can be pushed to 1500 ppm, 2000 ppm, 3000ppm, 4000 ppm, or any range between 1300 ppm and 4000 ppm with suitableresults. Within the range of 1300 ppm to 4000 ppm, it has been foundthat 1500 ppm to 2000 ppm is the most practical for commercial alloys.

While some helpful effects of oxygen at the surface such as increasedwear resistance or fatigue performance are understood, adding oxygen tothe bulk via oxidation is very challenging and time consuming,particularly because these alloys are designed to form coherent coatingsat the surface. Further, introducing oxygen via diffusion of the oxygenfrom the surface will introduce a strong gradient or oxygen contentacross the section of the part.

The Ti—Zr—X—Y formulation where Y represents an alpha stabilizerselected from the group including, but not limited to, aluminum, tin,silicon, oxygen, carbon, and nitrogen may be further improved bylowering the level of Zirconium to allow for the addition of otherstabilizers to increase the transus strength and alpha content.Stabilizers may also be combined.

An alloy with the composition Ti-35Zr-10Nb-1Al-0.2O exhibited anultimate tensile strength of 166 ksi and a yield strength of 144 ksiwith an elongation of 8 percent. An alloy with the compositionTi-30Zr-10Nb-1Al-0.3O exhibited an ultimate tensile strength of 170 ksi,a yield strength of 150 ksi and an elongation of 8 percent. An alloywith the composition Ti-30Zr-10Nb-1.5Sn-0.2O exhibited an ultimatetensile strength of 165 ksi, a yield strength of 143 ksi and anelongation of 8 percent. An alloy with the compositionTi-30Zr-2Mo-1.5Sn-0.26O exhibited an ultimate tensile strength of 155ksi and a yield strength of 137 ksi with an elongation of 12 percent. Analloy with the composition Ti-30Zr-4Mo-1.5Sn-0.25O exhibited an ultimatetensile strength of 166 ksi, a yield strength of 151 ksi and anelongation of 10 percent. All of these are useful alloys having greaterstrength than the conventional Ti-35Zr-10Nb alloy. The mechanicalperformances of these materials are detailed in the table of FIG. 4.

Zirconium is considered the agent that creates the black color uponblackening, and it is understood that increasing the zirconium contentwill increase the degree of blackening. It has been discovered however,that similar levels of blackening can be achieved with less zirconiumwhen aluminum is present. Between zirconium levels of 20 and 33 percent,it was found the addition of aluminum increased the blackeningperformance such that the aluminum containing materials blackenedequivalently or better than the no aluminum containing counterparts.This is important because in addition to strengthening the alloy, thealuminum can also serve to decrease the density and reduce the rawmaterial cost. The graph of FIG. 2 depicts decreasing lightness withincreasing zirconium content. Lightness is measured using the StandardCIELAB color space method and decreasing lightness is interpreted asincreasing blackness. At all points in this range, the aluminumdecreases the lightness. Alternatively stated, aluminum can increase theeffectiveness of the zirconium as a blackening agent.

During development it was determined that items having a lightness indexof 46 or lower were acceptable from an aesthetic viewpoint. While thisis obviously a subjective number, and others may find an acceptablelightness index limit less than 46, for example 42, it is helpful toguide the evaluation of different formulations. Likewise, others mayfind a lightness index of 48 to be acceptable. The effects of zirconiumcontent on lightness in this context is shown in the graph of FIG. 2.

In addition to the alloys having the formulation Ti—Zr—X, similarblackening behavior can be achieved with binary alloys of Ti—Zr. Thesealloys are generally more prone to ignition during blackening andrequire more complex processing conditions such as tightly controlledatmospheres or use of molten salt baths to control the oxidation. Byadopting the Ti—Zr—Y formulation, similar gains in mechanicalperformance and powder metal processability can be achieved with theelevation of the transus via additions of alpha stabilizers such asaluminum, tin, oxygen, nitrogen and carbon.

The choice of passivating elements can be made based on several factors,among them perceived biocompatibility, beta solution strengtheningeffects, economy, or different blackening behavior. Preferredpassivating elements include niobium, molybdenum, chromium, or vanadium.Other elements may work as passivating elements, as an example, tungstenor tantalum might be used, but the high cost and high density of thesematerial would preclude them from being preferred passivating elements.Testing has indicated that chromium, molybdenum, and vanadium, are allmore effective passivating agents than niobium. At an atomic percentageof 6.5 percent chromium, molybdenum, and vanadium, all samples yieldedlower lightness index values at the same zirconium content.

Although niobium has been used predominantly in the Ti—Zr—X alloys, thismay be because many of the prior examinations were from the perspectiveof suitability for medical implants. Molybdenum, chromium, or vanadiumare all suitable choices for passivating agents and can lower the costof the alloy without effecting the hypoallergenic nature of titaniumalloys. Further, the passivating elements can be combined to manipulatethe blackening behavior.

The use of molybdenum, although it lowers the beta transus temperature,is especially advantageous in these alloys as it can function as apassivator and a strong beta solution strengthened. This advantage isfurther developed as molybdenum containing alloys show increasedblackening behavior over alloys with the same atomic percentage ofniobium. Since alloys containing molybdenum can achieve the same degreeof blackness using less zirconium, more room for alpha stabilization viaalpha stabilizing agents is enabled, and at the same time providing morebeta solution strengthening due to the higher potency of molybdenum overelements such as niobium and vanadium.

A typical Ti-35Zr-10Nb alloy undergoes a heat treatment cycle in whichthe quenched beta phase is aged to enhance the strength of the material.The material can then be subject to many different and possibly repeatedblackening processes, potentially degrading the designed mechanicalresponse of the alloy. In an alloy densified by powder processingmethods, the full microstructure has been developed upon sintering orHIPing and further heating cycles to blacken the material will onlyserve to coarsen grains, which will not have a large effect onmechanical properties if properly controlled, especially if the alloyhas a higher beta transus temperature due to the addition of alphastabilizers.

The increased alpha stabilization of these alloys also allows them tobetter respond, to thermochemical treatments such ashydrogen-chemical-treatments and others. This advantage is developed asthe beta transus temperature of the alloy is increased due to thepresence of the alpha stabilizers. This allows better control over theequilibrium levels of hydrogen during the hydrogenation step of thethermochemical treatment, which must be kept below the point at whichtitanium hydride precipitates form, cracking the part. The elevatedlevels of the beta transus are also beneficial during thede-hydrogenation step of a hydrogen-chemical-treatment, where thehighest temperature that is below the beta transus is desired to aid inhydrogen removal. This step of hydrogen removal is difficult attemperatures equal to or below that of typical beta stabilized alloyscontaining only zirconium and passivating elements. Due to the nature ofthe thermal profiles used in powder processed materials, the ability toemploy these types of strengthening treatments furthers the degree ofmicrostructural control possible in the net shape manufacture ofarticles and also increases the mechanical properties, including dynamicfatigue performance.

While both tin and aluminum can be used as an alpha stabilizer there arenuances that can dictate which might be a better choice in certainconditions. An important consideration in these materials is blackeningresponse, or how readily the material becomes black during oxidation,and how dark the black is. At lower zirconium levels materials usingaluminum as an alpha stabilizer exhibit better blackening response thanmaterials using tin as an alpha stabilizer, however this trend isreversed at higher zirconium levels. In both cases the alpha stabilizedmaterial preforms better or equivalent to the beta stabilized material.

As shown in the graph of FIG. 3, aluminum stabilized material exhibitsbetter blackening response from about 20 weight percent zirconium up toabout 29 weight percent, including 22 weight percent and 25 weightpercent, at which point materials stabilized with tin begin to exhibitbetter blackening behavior. That said, 35 weight percent zirconium hasbeen found to be a practical upper limit for commercial titanium. Allcurves are for systems using 10 weight percent. Niobium as a passivator.

Improved blackening performance can also be interpreted as improved wearperformance. While the thicknesses of the black oxide layers aredifficult to measure, their wear resistance can be gauged by thenano-indentation measurements, As an example, a Ti-30Zr-10Nb alloydemonstrated a nano-indentation hardness of 1800 on the Vickers scalewhile a Ti-1.5Sn-30Zr-6Mo alloy demonstrated a hardness of 2000 on theVickers scale. Other Ti—Zr—X and Ti—Zr—X—Y alloys may demonstratesimilar hardness values.

As previously discussed, molybdenum is a potent beta stabilizer and alsoprovides for better blackening performance than material stabilized withniobium. It can be used at lower levels and is substantially lessexpensive than niobium. In a system with using 1.5 weight percent tinand 0.3 weight percent oxygen as the primary alpha stabilizers,molybdenum works well over a range of usage levels and providesflexibility in the materials performance. The mechanical performances ofthese materials are detailed in the table of FIG. 4.

Additions of molybdenum as a beta-stabilizer and passivator steadilyincrease the strength of the alloy. As shown in the table of FIG. 4, therange of two to four percent molybdenum provides strengths at least asgood as the Ti-6Al-4V alloy. As is to be expected, elongation decreasesslightly as strength increases. Unlike the Tiadyne™ 3510 Annealed andBlackened alloy, these alloys demonstrated similar yield strengths afterblackening. These are tabulated in the table of FIG. 5.

Molybdenum also performs well as a passivating agent and when combinedwith tin as an alpha stabilizer outperforms niobium on a weight basiswith respect to nano-indentation values, which are used as an indicationof wear resistance. As an example, a Ti-30Zr-10Nb alloy develops aVickers hardness of 1800 after blackening, but a Ti-1.5Sn-30Zr-6Mo alloydevelops a Vickers hardness value of 2000.

To evaluate the individual effects of passivator elements on blackeningbehaviors, several formulations using different passivating elementswere tested. The result of the effect of the different passivatingelement are shown in the graph of FIG. 6. All of the element tested wereadded at 10 atomic weight percent.

Also considered were titanium alloys containing zirconium and X, and analpha stabilizer selected from aluminum, tin, silicon, oxygen, carbon,and nitrogen, capable of being blackened in an air, oxygen, or nitrogencontaining environment to a lightness value of 48 or lower on the CIELABcolor space and having a beta transus temperature of 610° C. or greater,where X is shown in the table of FIG. 7.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

We claim:
 1. A titanium alloy comprising a Ti—Zr—X—Y formulation,wherein X is a Group V or Group VI metal and Y is an alpha stabilizerselected from, aluminum, tin, silicon, oxygen, carbon, and nitrogen;and, wherein said titanium alloy is capable of being blackened in anair, oxygen, or oxygen containing environment.
 2. The titanium allow ofclaim 1, wherein said alloy has a yield strength of at least 100 ksi. 3.The titanium alloy of claim 1, wherein Y is oxygen and an oxygen levelof said alloy is above 1300 ppm.
 4. The titanium alloy of claim 1,wherein a Zr content is greater than 22 weight percent.
 5. The titaniumalloy of claim 1, wherein a Zr content is greater than 25 weightpercent.
 6. The titanium alloy of claim 1, wherein a Zr content isbetween 20 and 35 weight percent, said alloy further comprisingaluminum.
 7. The titanium alloy of claim 1, wherein said titanium alloyhas a lightness index of 42 or less on the CIELAB scale.
 8. The titaniumalloy of claim 1, wherein said titanium, alloy has a lightness index of46 or less on the CIELAB scale.
 9. The titanium alloy of claim 1,wherein an aluminum equivalent of said alloy is less than approximately10.
 10. The titanium alloy of claim 1, wherein a transus temperature ofsaid alloy exceeds 610° C.
 11. The titanium alloy of claim 1, wherein Yis oxygen and an oxygen level of said titanium is between 1300 ppm and4000 ppm.
 12. The titanium alloy of claim 1, wherein an oxygen level ofsaid titanium is between 1500 ppm and 3000 ppm.
 13. The titanium alloyof claim 1, wherein said alloy is 22 to 35 wt % Zr, 0 to 10 wt % Nb, 0to 10 wt % Mo, 0 to 6 wt % Cr, 0 to 6 wt. % V, 0 to 5% wt % Al, 0 to 6%Sn, 0.13 to 0.40 wt % O, with the balance titanium.
 14. The titaniumalloy of claim 1, wherein said alloy is one of: Ti-30Zr-2Mo-1.5Sn-0.18O,30Zr-2Mo-1.5Sn-0.26O, Ti-30Zr-4Mo-1.5Sn-0.18O, 30Zr-4Mo-1.5Sn-0.26O,Ti-35Zr-10Nb-0.24O, Ti-35Zr-10Nb-1Al-0.15O, Ti-35Zr-10Nb-2.5Al-0.23O,Ti-30Zr-10Nb-0.2O, Ti-30Zr-10Nb-2Al-0.21O, Ti-30Zr-10Nb-1Al-0.3O,Ti-30Zr-10Nb-0.5Al-0.22O, Ti-30Zr-10Nb-1.5Sn-0.20O,Ti-30Zr-10Nb-3Sn-0.28O, Ti-30Zr-10Nb-6Sn-0.20O, Ti-30Zr-3Cr-1.5Sn-0.25O,and Ti-30Zr-6V-1.5Sn-0.25O.
 15. A titanium alloy comprising a Ti—Zr—X—Yformulation; said alloy capable of being blackened in an air, oxygen, oroxygen containing environment to a lightness value of 48 or lower on theCIELAB color space; wherein, Y is an alpha stabilizer selected fromaluminum, tin, silicon, oxygen, carbon, and nitrogen; wherein, X is abeta stabilizer selected from niobium, chromium, molybdenum, andvanadium.
 16. The titanium alloy of claim 15, wherein when X is niobium,said alloy has a transus temperature of approximately 640° C. orgreater; and when X is chromium, molybdenum, or vanadium, said alloy hasa transus temperature of approximately 610° C. or greater.